What fades first when you stop
Detraining is the reversal of training adaptations once the stimulus is removed. Strength is relatively durable in the short term, often holding for a couple of weeks before measurable decline begins, partly because much early strength comes from neural adaptations that persist for a while. After that initial buffer, performance tends to fall gradually over the following weeks.
Cardiovascular fitness markers, such as the gains in aerobic capacity, generally decline faster than maximal strength, with noticeable drops within the first weeks of inactivity.
Size versus strength on different timelines
Muscle size (hypertrophy) usually shrinks more slowly than strength is lost, so visible muscle persists for a time even as performance dips. The good news is that previously trained muscle tends to rebuild faster than it was first gained, an effect linked to retained myonuclei, sometimes described as muscle memory.
Exact rates depend on training history, age, activity level, and nutrition during the break, so figures here are general ranges rather than fixed numbers. This is general educational information, not medical or training advice.